Hi, I am still working on my quest to identify remote memory accesses using perf. I am confused about the LFB samples collected wit "perf mem rec". According to this Intel blog http://software.intel.com/en-us/blogs/2010/11/11/utilizing-load-latency-event-in-performance-monitoring-to-get-line-fill-buffer-breakdown one could use the weight information gathered by the hardware to identify "the potential data sources of LFB sample events".
In my experiments I get LFB samples with weight equal or greater than local RAM samples, I should I interpret these values ? Moreover, because I am more interested in identifying remote memory accesses sources than in effective load latency weight, I am wondering if using the perf mem tool (using the MEM_INST_RETIRED.LATENCY_ABOVE_THRESHOLD event) is the best solution. Couldn't I use sampling on other events such as UNCORE ones more easily and efficiently ? Thanks again for your help, Manu 2013/12/16 Manuel Selva <selva.man...@gmail.com>: > Thanks again. > > I guess that by "how you configure perf" you are speaking about > thred/cpu, kernel/user parameters ? For now I am monitoring one > application only on a given node only and I am trying to setup things > in order to get useful results independently of the overhead. I'll > investigate overhead in a second time. > > I can't use perf stat because I need to relate perf events with my > application's code. > > Manu > > 2013/12/16 Andi Kleen <a...@firstfloor.org>: >> On Sun, Dec 15, 2013 at 11:03:13PM +0100, Manuel Selva wrote: >>> Thanks for the answer Andi. >>> >>> Is there any way (I couldn't find in the Intel documentation) to >>> have an approximation of the "maximum" acceptable frequency ? >> >> It depends on how much overhead is acceptable and how you configure >> perf (which affects the cost of the handler) and what the executed >> code does. You could tune it to minimize throttles. >> >> I would start with something like 20003 >> >> If you only want the relative ratios of course using perf stat would >> be better. >> >> -Andi >> >> -- >> a...@linux.intel.com -- Speaking for myself only. >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-perf-users" >> in >> the body of a message to majord...@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
